Sagging roof in Mount Gravatt, a Southern suburb of Brisbane.

Inspected by Peter Weddell, owner/operator of Qld Home Buyers Inspection Service and Queensland Building Inspection Service, QBIS.

Considerable sagging to corner of roof (hip) due to insufficient support to part of the roof structure.



Props supporting this under-purlin (horizontal timber member, between the props) are too widely spaced the purlin is also undersize.


This can be rectified by fitting addition props for support, provided they are supported off an internal wall or an appropriate size beam.

Important note:

  • Purlin props must be supported off the internal walls, not the ceiling joists otherwise the ceilings will sag.
  • Alternatively a strut may have to be fitted, with support off the top of the external wall and propped off another nearby wall, if reasonably close by.


Poor method of construction:

Considerable sagging of hanging beam. This is also causing sagging to the ceiling of the living area below.


Weight from the roof is causing beam below the purlin props to tilt. The beam requires blocking or bracing to avoid further tilting.

Sagging roof in Mount Gravatt.


  • The roof structure being supported off an undersize hanging beam.
  • Undersized binders were also sagging from their span being too great, above a living room.
  • Sagging of the under-purlin (between the props) from props being too widely spaced.

Worth Considering:

In some cases, rather than going to the expense of restructuring the roof, it would be worth considering replacing the roof tiles with metal sheeting.


  • Having a new roof.
  • Choices of color.
  • Metal sheeting has far fewer joints therefore is less likely to leak.
  • Offers the opportunity of fitting insulation below the roof sheeting.
  • Would not require restructuring.
  • In some cases, cheaper than restructuring.


  • Can be noisy in heavy rain.
  • More prone to being damaged from hail.
  • Would require more securing of the structure to avoid uplift in a storm.

For independent Building Inspections Brisbane in all suburbs, Qld Home Buyers Inspection Service.